As a method of supporting the driving by providing auxiliary information on the driving to a driver of an automobile, a car navigation system is generally used for displaying path information in a several-inch-sized display provided near the center of an instrument panel (dash board). Furthermore, there is known a method using a head up display (hereinafter, referred to as HUD) which projects a predetermined image (virtual image) as information for supporting the driving and avoiding a risk in addition to the path information onto a front window shield glass (hereinafter, referred to as a front shield) or a reflection plate (referred to as a combiner) of a half mirror provided in the front shield as a screen in order to avoid that the safety is lowered when the driver turns his/her eyes.
As the related art, for example, Patent Document 1 discloses a technique in which information for supporting the driving or avoiding the risk is acquired and notified to the driver using the HUD. The publication discloses a method of detecting the information of a distance and a direction of an obstacle outside a vehicle (normally the front side) using a laser radar, a millimeter wave radar, a stereo camera, or the like, and determining the obstacle by an image recognition. In addition, disclosed is a display device which is provided with “a virtual image control unit which displays the virtual image such that the virtual image moves onto a path surrounding the obstacle when viewed from the driver in a case where the risk level set by the risk level setting unit is in a predetermined range, and changes a display method of the virtual image according to the risk level (see claim 1 etc.).
In addition, Patent Document 2 has an object to provide “a vehicle head up display which can short a time taken for turning the eyes of the driver by changing a display distance of the virtual image, and achieve a high safety preventing an accident in advance”. Regarding the object, there is the description “the vehicle head up display includes a light source, a scanning unit which performs a two-dimensional scanning using the light from the light source, a screen which forms the scanning light, and a projection unit which projects a video on the screen. A movable mechanism which changes a position of the screen is provided” (see Abstract).